WASHINGTON (Reuters) – Oil and gas drilling in a vast northern Alaskan wildlife refuge the U.S. government has protected since 1960 moved a step closer to reality on Saturday with the passage by U.S. Senate Republicans of the tax bill.

Republicans attached a measure introduced by Alaskan Senator Lisa Murkowski to the tax bill to open a portion of Arctic National Wildlife Refuge, or ANWR. The 51 to 49 passage of the tax overhaul early Saturday was a “critical milestone in our efforts to secure Alaska’s energy future,” Murkowski said.

Democrats and environmentalists deplore the prospect of development in ANWR, home to polar bears and millions of migrating birds and where Gwich‘in natives depend on migrating caribou. Stitching ANWR legislation into the tax bill that only needed a majority in the 100-member chamber was a “back door move” that never would have passed as a stand alone bill requiring 60 votes, they said.

“Little wonder Senate Republicans rushed the vote: it wouldn’t survive the light of public debate,” said Rhea Suh, president of the Natural Resources Defense Council environmental group.

Talks on a final tax bill will likely begin next week between the Senate and the House of Representatives, which has already approved its own legislation.

President Donald Trump, a Republican who favors producing as much fossil fuel as possible for domestic consumption and exports, wants the chambers to reach a deal on the tax overhaul legislation before the end of the year.

Former President Dwight Eisenhower, a Republican, set aside the refuge in 1960. Former President Jimmy Carter, a Democrat, expanded it in 1980. But that year Congress established the 1002 area of the refuge for potential drilling after the Arab oil embargo and the Iranian revolution in the 1970s caused fears of fuel shortages.

The U.S. Geological Survey estimated in 1998 that the 1002 area, a 1.5 million acre portion in northwest coast of ANWR, holds up to 12 billion barrels of recoverable crude.

Twelve Republicans in the House who oppose ANWR drilling wrote a letter to leaders in the Senate and House late last week. They said the resources in the refuge “simply are not necessary for our nation’s energy independence” and that lawsuits would likely accompany any development.

Murkowski tweaked the legislation to include a sale of 7 million barrels of oil from the Strategic Petroleum Reserve to help pay for tax cuts, equal to about $400 million in today’s oil prices. She made the change after a Senate official determined the Interior Department would have to conduct environmental assessments before lease sales are held on the refuge. Drilling opponents hope the assessments could delay or prevent ANWR development.